You might peak at my 1973 Play Pac listed in the trailers for sale
area, although I'm not in the inland NW, but on the Oregon coast. Oddly, I bought this trailer almost 5 years ago in Spokane! We've hauled it into many back forest service roads in pursuit of my landscape photography business. Few of these trailers are insulated, and we added 1 1/2" of polystyrene to the interior after camping in cold around Baker, Oregon. We did not like waking up to rain in the trailer, from all the condensation that happened on the un-insulated ceiling!